Mitochondrial localization and photodamage during photodynamic therapy with tetraphenylporphines

The subcellular localization sites of TPP4 and TPPS1 and the subsequent cel lular site damage during photodynamic therapy were investigated in CT-26 co lon carcinoma cells using spectroscopic and electron microscopy techniques. The association of both porphyrins with the mitochondria was investigated and the implications of this association on cellular functions were determi ned. Spectrofluorescence measurements showed that TPPS4 favors an aqueous e nvironment, while TPPS1 interacts with lipophilic complexes. The subcellula r localization sites of each sensitizer were determined using spectral imag ing. Mitochondrial-CFP transfected cells treated with porphyrins revealed l ocalization of TPPS1 in the peri-nuclear region, while TPPS4 localized in t he mitochondria, inducing structural, damage and swelling upon irradiation, as shown by transmission electron microscopy. TPPS4 fluorescence was detec ted in isolated mitochondria following irradiation. The photodamage induced a 38% reduction in mitochondrial activity, a 30% decrease in cellular ATP and a reduction in Na+/K+-ATPase activity. As a result, cytosolic concentra tions of Na+ and Ca2+ increased, and the level of K+ decreased. In contrast , the lipophilic TPPS1 did not affect mitochondrial structure or function a nd ATP content remained unchanged. We conclude that TPPS4 induces mitochond rial structural and functional photodamage resulting in an altered cytoplas mic ion concentration, while TPPS1 has no effect on the mitochondria. (C) 2 000 Elsevier Science B.V. All rights reserved.